1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor.
2. Description of the Related Art
A large number of dielectric ceramic compositions composed mainly of BaTiO3, for example, have already conventionally been proposed as dielectric materials for a multilayer capacitor which do not become semiconducting even after firing under a low partial pressure of oxygen and which have flat temperature characteristics of a capacitance.
With development of electronic technology in recent years, electronic devices have increasingly become highly sophisticated in function and highly integrated, and conditions for use of a multilayer ceramic capacitor have increasingly become severe.
In particular, with higher integration of electronic devices, an ambient temperature of a multilayer ceramic capacitor mounted in the vicinity of a heat generating element such as a CPU operating at a high frequency has become increasingly higher than in a conventional example, and influence on reliability has been a concern.
On the other hand, in order to meet the demand for a small size and a larger capacitance of a multilayer ceramic capacitor as described previously, there is also a need for a decrease in thickness of a dielectric ceramic layer and for an increase in a number of dielectric ceramic layers.
Under such circumstances, both of a smaller size and a larger capacitance and improvement in dielectric strength have been demanded for a multilayer ceramic capacitor. Therefore, a dielectric ceramic composition having a high dielectric constant, flat temperature characteristics of a relative permittivity, and that is excellent in dielectric strength and reliability in spite of a decrease in thickness of a dielectric ceramic layer has been required as a dielectric ceramic composition to be used for this multilayer ceramic capacitor.
For example, in order to meet the demand described above, Japanese Patent Laying-Open No. 2005-132645 proposes a dielectric ceramic composition expressed by a composition formula: 100(Ba1-xCax)mTiO3+aMnO+bNb2O5+cSiO2+dRe2O3, where Re represents at least one metal element selected from among Y, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, and a, b, c, and d represents a molar ratio, and conditions of 0.01≦a≦5, 0.05≦b≦2, 0.4≦c≦8, 0.05≦d≦2.5, 0.01≦x≦0.20, and 0.99≦m≦1.03 are satisfied.
The multilayer ceramic capacitor containing the dielectric ceramic composition in Japanese Patent Laying-Open No. 2005-132645, however, has disadvantageously been great in changes over time in insulation resistance under high-temperature load and also has been insufficient in reliability.